I. Technical Field
The present invention relates to a 2-dimensional image display device, an illumination light source and an exposure illumination device and also to a video display device such as a video projector, a television receiver or a liquid crystal panel.
II. Description of the Related Art
In recent years, laser display devices using laser light sources have attracted more attention. Conventionally, color spectra of fluorescent materials are wide and only the subdued color can be obtained even upon displaying a single color in a television receiver using a cathode-ray tube. On the other hand, in a laser display device using laser light sources, it has become possible to display a very vivid image having high color purity by using laser light sources having suitable wavelengths since lights from the respective light sources are monochromatic lights.
FIG. 29 shows the schematic construction of a conventional laser display device. Lights from laser light sources 101a to 101c of RGB three colors are intensity-modulated by light modulation elements 106a to 106c in accordance with an inputted video signal, and multiplexed using a mirror 103 and dichroic mirrors 102a, 102b. The multiplexed lights pass through a condenser lens 107 and are scanned in x-direction by a polygonal scanner 104 and in y-direction by a galvanometer scanner 105 to display a 2-dimensional image on a screen 108. In the display of this construction, since the lights from the RGB light sources are monochromatic lights, it becomes possible to display a vivid image having high color purity by using laser light sources having suitable wavelengths.
On the other hand, the above laser display device has a problem of so-called speckle noise that is generated due to the use of laser light sources having high coherency as light sources. The speckle noise is fine nonuniform noise generated by the interference of scattered lights from the respective parts on the screen 108 when laser beams are scattered on the screen 108. In the above laser display device, this speckle noise was removed by vibrating the screen 108.
FIG. 30 shows the schematic construction of another conventional laser display device. Lights from laser light sources 100a to 100c of red, green and blue colors are incident on a light integrator 103 after having beam diameters thereof expanded by a beam expander 102. The light integrator 103 is an optical system for illuminating rectangular openings at the top of a spatial light modulation element 107 with uniform illumination intensity and has such a structure that two fly-eye lenses, in each of which rectangular unit lenses are arrayed in a 2-dimensional lattice, are arranged in series. Here, uniform illumination by the light integrator 103 is not described in detail.
The light having passed through the light integrator 103 illuminates the spatial light modulation element 107 through a field lens 108 and a diffusion plate 106 after passing through a condenser lens 112 (red and blue lights pass through after being reflected by a mirror 115). The lights of the respective colors modulated by the spatial light modulation element 107 are multiplexed by a dichroic prism 109, and a full color image is formed on a screen 111 by a projection lens 110.
Here, the diffusion plate 106 is a transparent substrate made of ground glass and gives a random phase distribution to the wavefront of the incident light in order to reduce the above speckle noise. If this diffusion plate 106 is oscillated by a diffusion plate oscillating mechanism 113, the phase distribution of the light projected on the screen 111 changes and the fine pattern of the speckle noise temporally changes as the diffusion plate 106 moves. If the diffusion plate 106 is oscillated so that a pattern change of the speckle noise is quicker than the afterimage time of an observer, the speckle noise is time-averaged by the observer's eyes and a high quality image free from noise is sensed. This state of speckle reduction is disclosed in detail, for example, in Japanese Journal of Applied Physics, Vol. 43, 8B, 2004.
However, in the former laser display device, the screen needs to be vibrated in order to suppress the speckle noise. Thus, it is not possible to use a fixed wall surface as a screen and to suppress the speckle noise by an optical system without vibrating the screen. Further, in the latter laser display device, the speckle noise can be suppressed by the optical system, but the beam expander 102, the light integrator 103 and the like are necessary to obtain uniform illumination, which complicates the optical system.